German Offenlegungsschrift No. 3,202,775 describes an adhesive plaster in which medicinal active ingredient elements are applied directly to an adhesive layer. The adhesive is on a carrier, and the entire system is protected with a releasable cover which is pulled off before use.
Although such as plaster can be produced economically, it has serious disadvantages which render it unsatisfactory in practice. On the one hand, because of interaction, inherent to the system, between the adhesive and the active ingredient, it is necessary both to adapt the adhesive to the formulation of the active ingredient and on the other hand to adapt the formulation of the medicinal active ingredient to the adhesive. In addition, because of the interaction between the active ingredient and adhesive the required storage stability of such a plaster cannot be met so that it cannot satisfy the strict governmental requirements for registration as a drug.
During prolonged storage under unfavorable conditions, the medicinal active ingredient frequently migrates into the adhesive, and, conversely, substituents of the adhesive migrate into the active ingredient formulation especially since an adhesive is not a chemically uniform substance but a mixture.
An object of the present invention is to provide a plaster which does not have the above-mentioned disadvantages of prior art plasters.